'79 550 w/ 650 head?

[Guest]

Is there somewhere I can go to find some solid info on this swap? I've been piecing together bits and bobs from around here and Google, but I'd like to find some more comprehensive info.

[Toasty]

There's a few people on here who have done it, I'm most of the way through doing mine. I can make a list of things to know from what I've gathered.

- You have to make clearance in the bottom end for the 650 cylinder sleeves, it will slide down about halfway and then bind on the holes for the 550 cylinders and further down in the block

- Since the stroke is the same for the 550 and 650 no modifications to the crank are needed

- If you use a 650G donor engine you MUST use either the original 550 cam gears or 650E (hard to find).

- You can use the 650 cam (with smaller 550/650E cam gears) for more mid range or 550 cams for more top end punch. If you want to use 650 cams you'll need to drill the 550 gears, get some good drill bits because it's hardened steel. The 650G crank uses more teeth then the 550 so you will destroy your valves if you don't use the right gears.

- IIRC, the 550 ignition advance works just fine with the new head. The 650 unit can work but may need tuning to prevent pinging.

- You will have to rejet your carbs to 650 specs, or buy 650 carbs.

- If you want to use 550 headers you will need sleeves for the ends that fit into the cylinder head, otherwise it will sit loose.

- Externally it will be the same dimensions so there is no custom work needed to mount the engine.

- You'll get the updated combustion chamber from the 650 motor with the roller bearing 6 speed bottom end of the 550, win win.

[Pendulum]

Thanks! So from your post it looks like I should be looking for a 650G engine, with exhaust header, to make things as easy as possible? Thanks again. This is exactly the type of info I was looking for.

[Steve]

And, actually, it's not the head you are looking for, but the cylinders and pistons.

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[Pendulum]

And, actually, it's not the head you are looking for, but the cylinders and pistons.

.

D'oh! I knew that... I guess I reverted to my days of building Honda drag cars. Head swaps are very popular on those cars.

[Pendulum]

So I haven't found any info on what rods to use, but I'm assuming I use the 550 rods with 650 pistons. If so, do I have to make any adjustments to get everything fitted together?